Posted
by
Soulskillon Tuesday January 21, 2014 @04:01PM
from the now-we-just-need-some-dilithium-crystals dept.

An anonymous reader writes "Matter and antimatter annihilate immediately when they meet, so aside from creating antihydrogen, one of the key challenges for physicists is to keep antiatoms away from ordinary matter. To do so, experiments take advantage of antihydrogen's magnetic properties (which are similar to hydrogen's) and use very strong non-uniform magnetic fields to trap antiatoms long enough to study them. However, the strong magnetic field gradients degrade the spectroscopic properties of the (anti)atoms. To allow for clean high-resolution spectroscopy, the ASACUSA collaboration developed an innovative set-up to transfer antihydrogen atoms to a region where they can be studied in flight, far from the strong magnetic field (scientific paper)."

Parent and GP's suggestions might work in SF, but in real physics, a powerful laser blast will just break the ordinary matter into smaller pieces, which will still be sitting in the way. As for the positrons, they won't quite annihilate the ordinary matter; some of them would annihilate with electrons, but most of them would convert neutrons into protons, if I remember the nuclear chemistry chapters of my bachelor's courses correctly. The resulting unstable cores would either decay or fission, but the products would still be ordinary matter, and no matter (pun not intended) how long you keep repeating this, there would still be a lot of ordinary matter left that cannot be converted to energy any further by bombarding with positrons. </humorless pedantic nitpic>

In light of previous conversations with GP, I'm almost certain it's a joke, and/or he or she is testing my sense of humor. As for the moderation, it hasn't been modded at all, as you can see by clicking on the score. If you create an account, your posts automatically start at +1. If you make a significant numbers of interesting/informative/insightful comments and very few troll/flamebait comments, you automatically accumulate "karma", and if your karma is high enough, you get an additional +1 on top of that

Here's a serious answer, just in case you're not going along with the joking tone of the 2 posts I replied to...

I thought we were (implicitly) talking about the presence of air making terrestrial use of the weapon impossible. Particles coming loose tend to fly around at high speeds is somewhat random directions. Some of them will remain in the way of the antimatter projectile/beam, some of them will go out of the way but hit a molecule and return where they came from, some of them will create some backscatter effect (like a billiard ball being launched at high speed on a pool table full of other balls), causing molecules of air to get into the way. Even if one could fire a hypothetical ray that clearly annihilates all matter ahead of an antimatter projectile/beam, air would quickly rush into the vacuum being created (of course, having such a ray at one's disposal would mostly remove the point of using an antimatter projectile/beam). Whatever happens, there won't be the necessary hard vacuum for the antimatter projectile/beam to proceed. Even air at very low density would exert an incredibly strong braking/beam dispersal force because of the energy released when it collides with antimatter.

Also, in the present discussion, gravity is far too weak a force to be relevant at all. If you have to wait for gravity to remove stuff out of the way, air will have been given time to take that stuff's place a hundred times over. That's why there's no hard vacuum behind objects in (subsonic) free fall. Now in space, there is no air, but little gravity either...

The solar wind might not be all that dense [hypertextbook.com], but I still wouldn't chance the antimatter finding a random ion too close to the launcher.

Depending on the altitude, there's more up there than just the solar wind. The escaped particles from the ionosphere, for one.

Much of the space environment around the earth (in fact in the whole universe) contains plasma at varying densities. Whether an antimatter beam could travel very far in earth orbit would depend on its flux and the ambient mean-free path for the antimatter particles in question. I'm not sure what the numbers would be for antimatter, but some quick Googling reveals that non-exotic m

Jokingly, every blackhole could be composed solely of antimatter and the universe would be no different. Except, well, actually this statement is true --- every blackhole could be exclusively made of antimatter, because beyond the event horizon the contents of a blackhole cannot interact with the rest of the universe except gravitationally.

Note that it can settle in the lungs, if you inhale too much and can't exhale it you can suffocate. You won't feel it either because the CO2 will rise and exit the lungs. If you experiment with breathing it in, stand on your head after a few seconds and breathe out/in deeply.

Note that it can settle in the lungs, if you inhale too much and can't exhale it you can suffocate. You won't feel it either because the CO2 will rise and exit the lungs. If you experiment with breathing it in, stand on your head after a few seconds and breathe out/in deeply.

One of the most interesting physics papers I've read in recent years. Does away with dark matter by presuming that antimatter has the opposite gravitational sign as matter (which pops out very naturally once you apply CPT to general relativity).

As the electromagnetic force is almost 10^40 times stronger than gravity, it would be virtually impossible to test with anti-protons or positrons. But with electrically neutral anti-hydrogen, it becomes potentially testable.

Me neither. Things are often helped if people even just read the abstract they're talking about.

"Assuming that a particle and its antiparticle have the gravitational charge of the opposite sign, the physical vacuum may be considered as a fluid of virtual gravitational dipoles. Following this hypothesis, we present the first indications that dark matter may not exist and that the phenomena for which it was invoked might be explained by the gravitational polarization of the quantum vacuum by the known baryoni

Polarized gravitation would also make some forms of man-made time travel possible, which would be quite interesting. It would be very revolutionary if antimatter turned out to have opposite gravitational sign. Unfortunately, we're probably still several years from knowing. Still exciting, though.

You are mistaken. Antimatter cannot have the opposite gravitational sign as matter in general relativity. If it did, it would be possible to distinguish between an experiment performed in a gravitational field (e.g. standing on earth, antimatter released in a vacuum chamber would "float up") and an experiment performed in an accelerating rocket (e.g. antimatter released in a vacuum chamber would be "left behind" and would "fall down").

You may be familiar with the fact that light is affected by gravitation

You are mistaken. Antimatter cannot have the opposite gravitational sign as matter in general relativity. If it did, it would be possible to distinguish between an experiment performed in a gravitational field (e.g. standing on earth, antimatter released in a vacuum chamber would "float up") and an experiment performed in an accelerating rocket (e.g. antimatter released in a vacuum chamber would be "left behind" and would "fall down").

It's an assumption that that is true, not a proven thing. We don't know if the gravitational mass of antimatter has the same sign as the inertial mass of antimatter, nor do we know why those two quantities have the same sign (and value) as each other in normal matter. Accumulating enough cold antimatter to be able to measure gravitational effects at all is hard, as is explained elsewhere on this thread. Without the experimental evidence, no amount of armchair theorising is going to be truly sound.

I have been wondering how this would affect black hole evaporation through Hawking radiation. If it invalidates it, then we might want to be extra careful in the future about risking creating quantum black holes.

Well, it would if the "metaphor" I had heard about how Hawking radiation works were correct, but apparently it isn't [stackexchange.com]. While I won't say the explanation in the linked page makes sense to me (I probably couldn't follow the math anymore even if it was included), I must admit I had some similar concerns as Mr. Kujareevanich regarding that metaphor. If a gravitational well did result in the polarization of the gravitational dipole, then it would seem that perhaps it might affect the results. However if Hawking r

First, the impression I get is that they're hypothesizing that matter attracts matter, anti-matter attracts anti-matter, and matter and anti-matter mutually repel. We know that the first is true, the second is not testable until we can get enough anti-matter in one place to measure gravitational effects, and the third might be testable. Can we create a beam of positrons that's sufficiently slow, or travels sufficiently far, that we could measure its disp

"To allow for clean high-resolution spectroscopy, the ASACUSA collaboration developed an innovative set-up to transfer antihydrogen atoms to a region where they can be studied in flight, far from the strong magnetic field (scientific paper)."

Doesn't the anti-hydrogen have negative mass, so the combined mass of the hydrogen and anti-hydrogen would be 0? I understand that two photons are created, but I'm not quite sure where the energy comes from.

Nope. Quantum numbers are the opposite, but that's a more subtle thing, since there are particles -- including force carriers -- which are their own anti-particle (which immediately implies, for instance, that positrons and electrons are both influenced by magnetic fields in exactly the same way, just with opposite charge). Mass isn't a quantum number, but is rather... well, basically, a form of energy, so particles and their anti-particles have the same.

They turn into "energy", but it may not be very straightforward. Electrons and anti-electrons (positrons) usually annihilate to a pair of gamma rays - about as close to "pure" energy as you can get.

Anti protons and protons annihilate in a more ugly fashion since each is a bag of quarks. You can get pions that decay into neutrinos and muons which then decay into positrons and neutrinos. The muon decay is fairly slow - ~2 microseconds, enough for them to travel almost a kilometer.

In the end you get gamma rays, neutrinos (of various types), electrons and positrons. The combined energy (both their mass energy and their kinetic energy) of all the particles adds up to the original mass energy of the matter and antimatter, and any other energy put into the process.

Because protons and anti-protons are complex, it is very difficult to make anti-protons - only something like 1/100,000 collisions generates one, the rest just make pions and other junk. Then once you have the anti-protons its difficult to slow them down enough and cool them to where they will combine with the positrons. Is a very impressive and complicated experiment.

BTW- it is not a path to any reasonable energy storage, the efficiency of making anti-protons is much too low. I don't know of any even design concepts that would have usable efficiency.

Sure. When a bunch of Mongols fight a bunch of Hell's Angles, no body mass is lost, some of the mass ends up as blood splatters, some as body parts. If motorcycles are used in the fight, the the total mass energy of the bike-bits will be the same as the starting mass energy.

1) is true2) is true3) is true... but incomplete, and slightly misunderstands the nature of electromagnetism

electromagnetism is a force carried by photons between protons and electrons -- or between antiprotons and anti-electrons (which are also called positrons). since a photon is its own anti-particle, it's the same force. so we can use *electric* currents to generate magnetic fields that control positronic currents or the movement of charged antimatter.

One symmetry that has so far avoided any signs of breaking is the so-called CPT symmetry, which equates matter and antimatter at a fundamental level.

With this data analysis technique, they determined the antiproton’s magnetic moment to be pN=2.792845(12), which has equal magnitude, within experimental uncertainty, to the NIST CODATA recommended value for the proton magnetic mome

You can be against anonymous and in favor of pseudoanonymous without being a hypocrite.There is a huge difference between anonymous and pseudoanonymous.Pseudoanonymous allows users to be blocked, get a reputation either good or bad, and actuallyhave a presence. It's been shown that people are even more true to their real selfwhen using a pseudonym. That's completely different than the anonymous people thatpost stuff just to get a respond and would immediately be banned and/or ignored if they hada real acc